Population Viability Analysis of Puerto Rican Parrots: an assessment of its current status and prognosis for recovery.

Abstract

Despite 34 years of recovery efforts, the Puerto Rican Parrot continues to face a high risk of extinction. In 2002 the population count was estimated at 20-24 individuals, similar to post-hurricane Hugo counts (23) and close to the all time low count of 17-19 individuals in 1973. In light of this situation, coupled with discussions about establishing a second population in the karst region in north-central Puerto Rico, I reviewed cumulative demographic data collected over the past 13 years and conducted a population viability analysis to update the status and recovery outlook of the species. I used program Vortex to assess the status of the species and conducted a sensitivity analysis to assess the relative importance of selected parameters in the demography of the species. Basic Scenario model projections over 100 years were of a declining population (stoc. r = -0.066). Within 10 years the mean population (across extant populations) dropped from 40 to 24 individuals, and within 20 years, to 15 individuals. The persistence of the population was 0 and the mean time to extinction was 37.4 years. Sensitivity analyses indicated that almost none of the parameter values used in the model scenarios yielded a positive, mean stochastic growth. Low juvenile mortality (32% for age 0-1) produced the only positive average stochastic growth rate (r>0.02). Relative to the Basic Scenario model, the population grew only when productivity levels exceeded 2.5. Productivity levels recorded from 1990-95 (1.88 young fledged/active nest) and 1996-2002 (1.23young fledged/active nest) resulted in a steady population decline with very low persistence (0-3%). At the average productivity since 1990 (1.56 young fledged /active nest), supplementation temporarily boosted the mean population size. Once supplementations stopped, mean population size declined. The population continued to grow only when supplementation was coupled with sustained high productivity (e.g., 2.75 young fledged /active nest).

To augment the knowledge base of resident avifauna in north-central Puerto Rico, I collected information on the general biology of the Puerto Rican Woodpecker. The biology of the species was poorly documented, and its nesting habits might provide insights into what Puerto Rican Parrots may face when released in the region. Woodpecker detections were consistently higher in lower montane/shaded coffee plantation sites when compared to sites in karst topography. Management, past and present, in shaded coffee plantations may help explain the high number of detections in shaded coffee sites as compared to secondary forests. Management results in higher numbers of dead trees as trees are girdled routinely to 'create openings' in the shade. The onset of reproduction during my study was in January, with the majority of incubation occurring in February and March. The average observed clutch size was 5 eggs (n=6, SE=0.26), with only one cavity containing 4 eggs. Nest success varied greatly from year to year. In 1998, only 1 out of 7 active nests successfully fledged young, whereas in 1999, 7 out of 9 did so. Possible explanations for high chick mortality, particularly in 1998, were infestation of chicks with ectoparasites or dehydration and/or hyperthermia. There is no evidence, from this study or from literature, to believe that the status of the Puerto Rican Woodpecker is in danger. The value of this study lies primarily on augmenting the knowledge about the natural history of another endemic species.